In the past, there has been a variable inductor in which a position of a magnetic core with respect to a coil is changed by an external signal such that the inductance value of the coil can be changed. Such a variable inductor is used, for example, for adjustment of filter characteristic and resonance frequency in an LC filter and a resonance circuit.
In Japanese patent publication No, 2005-64308, it is disclosed with respect to a variable inductor in which magnetic flux is changed by moving a magnetic flux changeable means in the vicinity of an inductor and the inductance value is changed thereby.
In Japanese patent publication No. 2006-286805, it is disclosed with respect to a variable inductor in which the inductance thereof is changed by changing the frequency of alternate current to be applied.